Negative Bias Temperature Instability (NBTI) is a key reliability issue that is of immediate concern in p-channel MOS devices operating with negative gate voltages. This same mechanism also affects nMOS transistors when biased in the accumulation regime, i.e., with a negative bias applied to the gate. NBTI manifests as an increase in the threshold voltage and consequent decrease in drain current and transconductance. The degradation exhibits log law dependence with time.
In sub-micrometer devices, nitrogen has been incorporated into the silicon gate oxide to reduce the gate current density and prevent boron penetration. However, incorporating nitrogen enhances NBTI. For this reason, in new technologies, e.g., 32 nm and shorter nominal channel lengths, high-k metal gate stacks, are used as an alternative to improve the gate current density for a given equivalent oxide thickness (EOT). Even with the introduction of new materials like Hafnium Oxides, NBTI still remains a concern. In addition, Hafnium Oxide based metal gates exhibit Vtshift.
Vt-shift by oxygen-ingress is an issue causing Vt variation in high-k dielectric metal gate technology. It is believed that the Vt shift is due to two components: stable component and meta-stable component. The stable component refers to the removal of oxygen vacancies in HfO2 and the meta-stable component refers to the formation of oxygen interstitials in HfO2.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.